The present invention relates generally to Electrofax copy paper, and more particularly, to Electrofax copy paper suitable for use in dry toner, pressure fused photocopy machines such as those marketed by 3M Company under the tradename "VQC".
The Electrofax printing process preferably utilizes a paper substrate coated with a photoconductive zinc oxide coating that is normally an insulator in the dark. In the printing process, a blanket electrostatic charge is first applied to the photoconductive insulating layer. The charge may be stored on the surface for a time in the dark. The rate at which this stored charge is dissipated when kept in the dark is referred to as the dark decay rate. Within the period in which a substantial charge remains, a light image is focused on the charged surface, discharging the portions of the surface irradiated with light, leaving the remaining imaged areas in a charged condition and thereby forming an electrostatic image thereon. The electrostatic image is rendered visible by applying to the electrostatic image a developer substance, such as a pigmented thermoplastic resin powder toner. In the dry toner copiers, the toner is fused to the image with the aid of heat and pressure as the image sheet is passed between two steel rollers to fix the image thereon.
Conventional Electrofax paper comprises a multiple coated paper substrate with barrier and conductive coatings over which is applied a photoconductive zinc oxide coating. Electrofax basestock, as supplied to the coater where the photoconductive coating is applied, will generally include a treatment or treatments for conductivity and solvent holdout for a typical solvent based photoconductive coating.
Current methods of manufacture include building up conductivity in the paper substrate and then barrier coating as separate operations, or, saturating the paper substrate for both conductivity and barrier properties in one operation. It is generally believed by the industry, that, with paper as a substrate, both solvent holdout and conductivity is required in order to design an operable Electrofax copy sheet. This conclusion is amply supported in the literature as exemplified by the following list of prior art references, which is by no means intended to be complete. Moreover, there are no known literature references which contradict this conclusion.
U.s. pat. No. 2,979,402 PA1 U.s. pat. No. 3,116,147 PA1 U.s. pat. No. 3,639,162 PA1 U.s. pat. No. 3,672,982 PA1 U.s. pat. No. 3,798,032 PA1 U.s. pat. No. 3,870,559 PA1 U.s. pat. No. 3,887,496 PA1 U.s. pat. No. 3,907,738 PA1 U.s. pat. No. 3,953,374 PA1 U.s. pat. No. 3,971,680 PA1 U.s. pat. No. 4,007,148 PA1 T.a.p.p.i. december 1965, Vol. 48, No. 12, pages 77A-82A PA1 T.a.p.p.i. march 1974, Vol. 57, No. 3, pages 81-84 PA1 T.a.p.p.i. march 1974, Vol. 57, No. 3, pages 75-78 PA1 T.a.p.p.i. june 1975, Vol. 58, No. 6, pages 96-99
However, in accordance with the present invention, there is disclosed an Electrofax copy paper and method of manufacture which does not include the addition of any added ingredients to the basestock thereof especially for increasing its conductivity. The theory behind the preparation of Electrofax copy paper according to the present invention is related to a correlation between basestock conductivity and the conductivity of the photoconductive zinc oxide coating applied to the basestock.